Re: ECM Availability

[Garfield Willis <garwillis@msn.com>]

On Mon, 21 Aug 2000 20:31:05 -0700, Carl Summers <InTech@writeme.com>
wrote:

>I gotcha.....Are you thinking of an "easy" TPS vs rpm as a backup fuel???

We thot about that, but another MAP sensor is soooo easy to install,
(unlike dual TPSs), so instead of alpha-N for the backup, we just
stick with a rudimentary speed density, if we use a primitive backup
controller. The latest scheme where we run two complete ecms in
parallel, you common the non-critical sensors (like IAT & CTS), and
have redundant sensors for critical things like MAP and crank-pos.

We don't have the luxury of adopting the "backup sensor" strategy the
OEMs have; namely, revert to alpha-N via TPS, if MAP fails, for
example. Cuz we have to also guard against complete ecm failure. Hence
the differences between automotive and aircraft sometimes.

>What are you gonna do with the spark???let the module give it the extra???

Yup, turns out the built-in advance curve in the DIS module base is
adequate (mimics centrifugal advance only), cuz in aircraft, we don't
normally benefit from use of vacuum advance (not much
light-part-throttle ops). Soooo, if the primary ECM that's doing
fuelNfire looses it's marbles, the DIS module is sufficient for spark
advance; not to mention the fact that we have a way to run TWO DIS
modules together actively, but it's kinda messy with all them spark
wires and coil joiners. Some prefer the concept of firing pairs of
coil-per-plug, to keep the 'HV plumbing mess' down. That way if a coil
fails, all you lose is one jug. But you lose *some* full-redundancy
coverage compared to a full-up dual DIS system. But weighs less and
isn't such a tangle. Ahh, trade-offs.

With full active redundant ecms, and full redundant IGN, you would
have two MAP sensors, two crank sensors, two ecms, two DIS modules
(each populated with it's coils), and waste-fire coil joiners, along
with a real rat's nest of HV leads. But you also have a system that
"takes a licking, and keeps on ticking", as the old Timex advert used
to say. :)

>I
>know you'll do it right,,just gotta poke ya in the ribs once in a
>while...

Yeah, uh huh. I'd rather you tossed me a few barBQ'd poke ribs. :)

Gar


----------------------------------------------------------------------------
To unsubscribe from gmecm, send "unsubscribe gmecm" (without the quotes)
in the body of a message (not the subject) to majordomo@lists.diy-efi.org